The present invention relates to an image production apparatus, an image display apparatus, an image display method and an optical modulation device adjustment apparatus wherein a light diffraction modulation device such as, for example, a light valve device of the diffraction grating type which diffracts or reflects light is used to produce or display a two-dimensional image.
A method is known wherein, in order to assure a high resolution of an image on an image formation apparatus such as a projector or a printer, a light flux from a one-dimensional image display device is projected onto an image formation element while being scanned by an optical scanning means to form a two-dimensional image. The method is disclosed, for example, in U.S. Pat. No. 5,982,553 (hereinafter referred to patent document 1). As one of one-dimensional image display devices, a grating light valve (GLV) device developed by Silicon Light Machine of USA is known and disclosed, for example, in Japanese Patent No. 3,164,824 (hereinafter referred to as patent document 2) and U.S. Pat. No. 5,841,579 (hereinafter referred to as patent document 3).
The GLV device is formed from a diffraction grating of the micromachine phase reflection type which makes use of diffraction of light. Where the GLV device is used, an image can be displayed by electrically controlling the gradation of the light.
Typically, in the GLV device, a pixel element which forms a pixel is formed from several ribbon electrodes of several μm in size, and several hundreds to several thousands such pixel elements are disposed in a one-dimensional direction. The GLV device in the form of a one-dimensional image device which includes a plurality of pixel elements functions as a one-dimensional spatial modulator, and illumination light condensed in a one-dimensional direction is first modulated by the GLV device and then scanned in horizontal directions by means of a galvano mirror (polygon mirror) to form a two-dimensional image.
When compared with an ordinary two-dimensional display device, where the GLV device is used, also the number of pixels in a vertical direction of a screen is equal to the number of pixels in the one-dimensional direction. However, since only a width at least equal to the width of one pixel is required in the transverse direction, the number of pixels necessary for display of a two-dimensional image is small. The GLV device can be formed such that it has an active region of a comparatively small size and can achieve display of a high resolution, a high switching rate and a great band width. Meanwhile, since the GLV device can operate with a low application voltage, it is anticipated that a display device of a significantly reduced size can be realized.
When compared with an ordinary two-dimensional display device, for example, a projector type display device using a liquid crystal panel, an image display apparatus which uses such a one-dimensional image display apparatus as described above, that is, a GLV device, can represent a very smooth and natural image since the GLV device itself does not include a boundary between pixels. Further, if lasers of the three primary colors of red, green and blue are used as light sources for such GLV devices and lights from them are mixed, then an image having a very wide and natural color reproduction range can be represented. In this manner, an image display apparatus which uses the GLV device exhibits a superior displaying performance which cannot be achieved by the other conventional image display apparatus.
Actually, however, it is not easy to realize a good image display with full pixels of an image display apparatus for 1,080×1,920 pixels obtained by scanning a GLV device including, for example, 1,080 pixel elements. The reason is that usually it is difficult in production of devices to produce ribbon electrodes for formation of pixel elements uniformly in terms of the shape and the surface state over an overall display region. Therefore, also in a state wherein the pixel elements are at rest, unevenness of approximately nm is exhibited between the pixel elements. Therefore, a GLV device as a modulator exhibits different modulation characteristics (driving voltage-modulated light luminance) among different pixel elements. As a result, some ununiformity in luminance appears on a screen, and there is a problem that, for example, a uniform black image cannot be obtained.
Further, since driving circuits provided for the individual pixels for adjusting the gradation of luminance have some dispersion, it is not easy to make the modulation characteristics of the pixel elements uniform. For example, an error of a driving signal for moving a ribbon electrode at the nm level disperses the amount of movement of a movable ribbon electrode of the GLV device and gives rise to a variation in pixel element modulation characteristic.
Such dispersions in modulation characteristic are recognized as transverse stripes in a unit of one to several pixels on a display screen and causes deterioration of the picture quality.
Further, in order to illuminate a GLV device which is a one-dimensional image device, illumination light is condensed in a one-dimensional direction and is illuminated on a line on the GLV device. In this instance, it is not easy to make the illumination light intensity uniform over the overall illumination region. Even if uniform illumination can be realized by optical designing and initial adjustment, it is difficult to realize normally uniform illumination light due to an influence of a variation of a light source or an optical system arising from a temperature variation or a secular change. Although such ununiformity in illumination is not comparatively conspicuous where a single color is involved, where different colors are involved as in the case of a color image, the ununiformity in illumination is recognized as a color fault and deteriorates the picture quality. Particularly where different illumination systems are used for different colors as in the case of a laser projector, such ununiformity in color is liable to appear.
Further, there is the possibility that the picture quality may be deteriorated by processing of a driving signal to be applied to a pixel element.
Usually, a digital driving signal inputted from a circuit in the preceding stage is converted into an analog signal by a D/A (digital to analog) conversion circuit and then inputted to a driving circuit, whereafter it is applied to a pixel element.
Where the D/A conversion circuit and the driving circuit have a smaller bit width than the preceding circuit, when a signal of the preceding stage having a greater bit width is inputted to the D/A conversion circuit and the driving circuit, low order bits of the signal are cut and thinned out. Consequently, the signal exhibits comparatively discontinuous values, or in other words, the signal is quantized or digitized.
The signal quantized in this manner exhibits rougher gradations and has an error when compared with the driving signal in the preceding circuit. This is called quantization error.
The quantization error produces some discontinuity between pixels on a screen. Since the eyes of the human being have a high sensitivity, such small discontinuity between pixels is recognized as an unnatural display to the human eyes. Particularly on a display apparatus wherein light from a GLV device is scanned to form a two-dimensional image, through scanning of a one-dimensional image on the screen, an abnormal point of the one-dimensional image makes a transverse stripe on the screen, which is further likely to be sensed.
Further, an image display apparatus which employs a GLV device necessitates structural improvements such as an improvement in arrangement of a light source and optical parts in order to display a color video image of a high quality while it is miniaturized. Particularly where different illumination systems are used for different colors as in the case of a laser projector, there is a technical problem of how to reduce the size of a display apparatus while it is realized to synthesize the illumination lights of the different colors with a high degree of quality and remove unnecessary illumination light components efficiently to reduce noise to the illumination lights to be used to display an image.